I found supririsingly little information on the penalties for incorrect entries on a passcode-protected iPhone. So I decided to test it out myself. The only thing is I forgot to count the number of failed attempts. I believe this was after 8 failed attempts, but not sure.
It started with "try again in 1 minute", then 5, now 15. With the delay getting longer and longer, imagine having to wait an hour or more to try to use the phone. Hehehe, I like this feature a lot. We carry so much information on our phones, it's good that there's something to lock it down like this.